The present invention relates to a solar cell composed of a semiconductor body having a pn-junction, a rear contact provided on the rear side of the semiconductor body, and a system of contact fingers disposed between first and second anti-reflection layers on the front side of the semiconductor body, which is intended to be exposed to light.
In order to increase the conversion efficiency of silicon solar cells, they are provided with an anti-reflection layer on the side intended to be exposed to the light. This reflection reducing layer is composed of an insulating material and must therefore not cover the front contact provided on the prior art solar cells for their connection with other cells. The thickness of the reflection reducing layer is selected to be such that a reflection minimum occurs at a wavelength of about 600 nm. The layer is a .lambda./4 layer and has an index of refraction ranging from 1.4 to 2.5. The anti-reflection reducing layer reduces reflections at the solar cell surface from about 30% to less than 3% for the reflection minimum, so that solar cell efficiency is increased considerably. Two or more matched anti-reflection layers may further improve the reflection behavior.
U.S. Pat. No. 4,336,648 discloses a solar cell in which an anti-reflection layer completely covers the metallization of the front contacts of the solar cell. The electrical connection with these front contacts is effected by ultrasonic welding, with the reflection reducing layer disposed between the contact locations being locally removed during the welding process.
U.S. Pat. No. 4,694,117 discloses a solar cell in which a rear contact is disposed on a semiconductor body having a pn-junction. On the side that is intended to be exposed to the light, the semiconductor body is provided with a reflection reducing layer. At least one front contact is applied directly to an insulating layer so that the charge carriers travel from the semiconductor body to the front contact by tunneling through the insulating layer. The insulating layer simultaneously constitutes the reflection reducing .lambda./4 layer and may be composed of TiO.sub.x with a thickness of about 70 nm.
The front contact may be disposed above an additional ohmic metal terminal disposed underneath the reflection reducing layer and contacting the surface of the semiconductor body. The front contact may be composed of conductive adhesives, glued-on conductor paths, or glued-on wires.
Solar cells equipped with conductive anti-reflection layers on which the front contact fingers are disposed are also known. For example, U.S. Pat. No. 4,577,393 discloses a method of producing such a solar cell in which the pn-junction is produced by the diffusion of impurities from a doping layer. A first layer serving as a diffusion source for producing of the pn-junction and for doping the anti-reflection layer is applied to the semiconductor body. A second layer for producing the anti-reflection layer is then applied onto the first layer. A tempering process takes place in which the pn-junction is produced, an anti-reflection layer is formed of the two layers, and the anti-reflection layer is doped so that it becomes suitably conductive.